www.makemkv.com

For a few reasons, I'd love to be able to specify an alternate audio file while extracting a blu-ray.

For example:

Movie (Video and possibly subtitles) --> Movie.mkv
Audio --> Movie.mka

I'd like to do that in one pass. Ultimately, yes, I could use mkvextract the audio from the video and re-mux the video, but that can take a LONG time.

So, any chance of having a "File" in the dropdown of audio tracks and cause it to redirect that audio track to a separate container from the main movie?

MakeMKV makes video files... But there are other tools that will let you separate out the individual audio tracks, after the fact.